Extrusion machines are generally constituted by one or more screws driven in rotation inside an elongated sleeve in which are provided cylindrical bores for housing the screws. The latter are provided on their periphery with helical flights which drive in the downstream direction the material introduced through an upstream end of the sleeve. By acting on the pitch of the screws, the material can be subjected to different treatments, for example trituration, kneading or compression. The material is therefore driven to the downstream end of the sleeve which may be provided with an extrusion die or a simple outlet orifice in the case where the material does not have to be subjected to an extrusion.
In order to vary the treatment carried out in the course of the advance of the material through the sleeve, the screws are formed by successive regions having flights of different pitch and shapes. For example, conveying sections having a large pitch may be used or sections having a smaller pitch, or even the reverse arrangement for retarding and consequently compressing the material.
It is often necessary to modify the arrangement of the sections having different pitches, for example to change or adapt the treating procedure. Furthermore, the flights may deteriorated or be subjected to great wear, for example in the case where the conveyed material is particularly abrasive. This wear is of course greater in the most compressed regions.
Consequently, it is necessary to be able to change or replace certain sections of the screws.
For this purpose, the screws are usually formed by juxtaposed hollow sections mounted on a central shaft connected to a motor for driving the shaft in rotation. To ensure that the rotation of the shaft is transmitted to the screw sections, the latter are provided, on their inner wall, with grooves which are engaged with corresponding splines provided along the central shaft.
The distance between the axes and the guiding in rotation of the screws is usually ensured by a fixed bearing mounted at one of the ends of the shafts and by a floating bearing mounted at the other end .
Furthermore, the sleeve which surrounds said screws is constituted by a plurality of independent parts whose separation plane passes through the axis of the screws. This feature affords easy accessibility to the screws in position, which permits, among other things, checking of the surface of the flights, cleaning and repairs, and in particular the mounting and the removal of the screws.
Now, a complete screw which is constituted by sections stacked on the splined shaft represents a considerable weight.
Up to the present time, the mounting and the removal of the screws, and the replacement of the defective sections are carried out by equipment, which is maladapted and may result in the deterioration of the splines of the screw shafts when the sections are mounted and removed, and by a succession of long and fastidious operations.